1. Field of the Invention
The present invention relates to an optical disc recording method and access method, an optical disc, an optical disc recording apparatus and an optical disc apparatus.
2. Description of Prior Art
Conventionally, optical recording media such as a disc-shaped optical recording medium and a card-shaped optical recording medium have been developed and now available in market for utilizing an optical or magneto-optical signal recording/reproduction method. These optical recording medium include a so-called compact disc (CD), i.e., a read only memory (ROM) type recording media, and a so-called write once type (writable enabling a user to write a data once as well as a magneto-optical disc enabling a data rewrite (so-called overwrite).
An optical disc recording/reproducing apparatus for writing and reading out a data onto/from a disc-shaped optical recording medium includes a built-in laser diode for emitting a laser beam for recording/reproducing an information and a built-in photo detector for detecting a reflected light of the laser beam applied to an optical disc. According to the detection output from the photo detector, a focus servo and a tracking servo is executed to an optical head. The optical disc is rotated at a constant angular velocity or at a constant linear velocity by a spindle motor so that the optical head scans a record track on the optical disc with the laser beam, thus recording/reproducing a data onto/from the optical disc.
On the other hand, these years, a high capacity is realized in an optical recording medium such as a ROM (read only memory) disc and RAM (random access memory) disc. The semiconductor laser used for the optical head of the optical disc recording/reproducing apparatus is required to have a shorter wavelength and the objective lens for focusing the laser beam on the information record plane of the optical disc is required to have a high numerical aperture (NA).
In order to implement a high-density phase change type optical disc having a greater capacity than a DVD-RAM, there is known a technique to minimize the spot size. The spot size on the recording medium is generally given as .lambda./NA, which can be reduced by a technique to use a short wavelength laser source such as GaN and ZnSe and a technique to increase the objective lens NA by use of two-lense configuration such as a solid immersion lens (SIL).
For example, if .lambda.=640 nm and NA=0.85, the spot diameter on the medium is about 0.75 mm. In this case, if a signal is recorded or reproduced using RLL (1, 7) modulation for example, it ispossible to obtain a recording density of about 0.21 mm/bit.
Moreover, it is preferable to suppress a DC component of recording/reproducing signal in an optical disc system. Especially when removing PR for a high-density recording/reproduction, it is necessary to suppress the DC component as much as possible
Furthermore, in an optical disc system using an optical head having an objective lens of high NA, it is necessary to increase an error correction efficiency in order to suppress errors caused by dust and scars on the disc surface affecting the laser beam. In order to enhance the error correction efficiency, the code size is increased and the ECC block size is increased. Furthermore, there is a method of interleaving an error correction code into a block so as to spread an ECC block into one track on the inner circumference of the disc.
In this case also, access efficiency should be secured and a pre-address or the like is required more than a certain level.
In general, an address information for accessing an optical disc is recorded in advance in an address block provided as a reproduction-dedicated area in a head portion of a user data block where a user data is recorded/reproduced as a modulation code according to a predetermined modulation rule. The modulation code of the address information recorded in the aforementioned reproduction-dedicated area has been a modulation code of the same method as the user data recorded in the recording/reproduction area so as to simplify the reproduction system.
As a representative modulation method having a wide channel detection window which is appropriate for carrying out a high-density recording and reproduction, the RLL (1, 7) code and RLL (2, 7) code are known.
The RLL (1, 7) modulation is a modulation in which a pit information (symbol) 0 has the minimum run of 1 and the maximum run of 7, and the maximum reverse interval of a waveform sequence is based on the run length limited (RLL) code.
Here, in the RLL (1, 7) modulation, a data having a basic data length of m bits is converted into a variable length code (d, k; , m, n; r) as follows. For example, using a conversion table containing a code limiting a predetermined time of succession of the minimum run d of 0 of the channel bit string of the RLL (1, 7) code, a data having a basic data length m of 2 bits for example is converted into a variable length code (1, 7; 2, 3; 2) having the 0 minimum run d of 1 bit, the 0 maximum run k of 7 bits, the basic data length m of 2 bits, the basic code length n of 3 bits, and the maximum constriction length r of 2. This RLL (1, 7) modulation is carried out, for example, using a conversion table as follows. RLL (1,7;2,3;2)
Data Code i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000 100 001
In this RLL (1, 7) modulation, if the recording waveform sequence bit interval is assumed to be T, the minimum reverse interval Tmin is 2T. Moreover, if the data string bit interval is assumed to be Tdata, this minimum reverse interval Tmin is 1.33 (=(m/n).times.Tmin=(2/3)=2) Tdata. Moreover, the maximum reverse interval Tmax is 8(=7+1)T (=(m/n).times.Tmax) Tdata (2/3)=8 Tdata=5.33 Tdata). Furthermore, the detection window Tw is 0.67 (=2/3) Tdata.
Moreover, in the RLL (2, 7) modulation, a data having a basic data length of m length code (d, k; m, n; r) is carried out as follows. For example, using a conversion table containing a code for limiting a predetermined number of time of succession of the 0 minimum run d of the channel bit string of the RLL (2-7) code, a data having a basic data length m of 2 is converted into a variable length code (1, 7; 2, 3; 3) having 0 minimum run d of 2 bits, the 0 maximum run k of 7 bits, the basic data length m of 1 bits, the basic code length n of 3 bits, and the maximum restriction length r of 2. This RLL (2, 7) modulation is carried out, for example, by using a conversion table as follows. RLL (2,7; 1, 3; 2)
 Data Code i = 1 11 10 00 10 01 00 i = 2 011 00 10 00 010 10 01 00 000 00 01 00 i = 3 0011 00 00 1000 0010 00 10 0100
In this RLL (2, 7) modulation, if the recording waveform sequence bit interval is assumed to be T, the minimum reverse interval Tmin (=(d+1) T) is 3R. Moreover, if the data string bit interval is assumed to be Tdata, the minimum reverse interval Tmin is 1.5(=(m/n).times.Tmin=(1/2).times.3) Tdata. Moreover, the maximum reverse interval Tmax (=(k+1)T) is 8 (=7+1)T (=(m/n).times.Tmax) Tdata=(1/2)=8 Tdata =4.0 Tdata). Furthermore, the detection window Tw (=(m/n).times.T) is 0.5 (=1/2) Tdata.
On the other hand, in a magnetic field modulation magneto-optical recording method, as the minimum run length signal level approaches 0, line density is increased and for detection with he most likelihood decoding, because of the short minimum mark length, it has been difficult to form a high-quality pit in preparing an original recording disc by way of exposure. Moreover, in a phase change type and a magneto-optical type light intensity modulation recording where a land/groove recording of a high density is to be carried out, it has been difficult to obtain both of a fine groove width control and a short mark length formation.
For this, if the address block recording wavelength is increased, the channel clock frequency is difference between the address block and the user data block. Accordingly, it becomes necessary to provide a plurality of clock synchronization circuits for processing each of the signals separately or to provide a long pull-in portion for pulling into a difference frequency. This complicates a reproduction system as well as decreases the optical disc capacity.